There have already been known processes for producing xylylenediamine, which include hydrogenating phthalonitrile through a flow method employing a heterogeneous catalyst (i.e., trickle-bed mode).
One disclosed process is continuous catalytic hydrogenation through the fixed-bed method, in which phthalonitrile is reduced through catalytic hydrogenation under liquid-gas-solid tri-phase conditions in the presence of a heterogeneous nickel-copper-molybdenum catalyst (see Patent Document 1).
In the process for producing xylylenediamine which includes hydrogenating phthalonitrile in the presence of a heterogeneous catalyst through the fixed-bed method, the activity of the hydrogenation catalyst, which is a heterogeneous catalyst, is deteriorated rapidly, which is problematic. Therefore, when hydrogenation of phthalonitrile is performed for a long time through the fixed-bed method, the hydrogenation catalyst must be regenerated and activated.
Generally, in industrial production, the catalyst is required to have a catalyst life of at least one year. The catalytic performance such as catalytic activity is conceivably impaired, because of complicated factors. In the case of the hydrogenation catalyst employed in hydrogenation of phthalonitrile to produce xylylenediamine, the drop in catalytic activity is attributable to a plurality of factors. One conceivable factor is deposition on a catalyst surface of high-boiling-point organic by-products formed through polymerization or condensation. As used herein, the term “catalyst life” refers not to the period of time until the catalyst no longer exhibits catalytic activity, but to the period of time during which the catalyst can be continuously employed in industrial production.
The process for producing xylylenediamine through hydrogenation of phthalonitrile in the presence of a heterogeneous catalyst in the fixed-bed mode has a problem in that, in addition to a drop in catalytic activity, high-boiling-point by-products plug a part of the catalyst layer, to thereby increase inner pressure loss of the reactor (differential pressure in the catalyst layer), failing to supply phthalonitrile solution serving as a raw material and impeding continuous operation. Since continuous operation is impeded by deposition of high-boiling-point by-products on the catalyst layer, the high-boiling-point by-products deposited on the catalyst layer must be removed.
In conventional processes for producing xylylenediamine, one known means for regenerating and activating the catalyst is hydrocracking. In one specific procedure, the catalytic hydrogenation catalyst which has been employed in hydrogenation of dicyanobenzene (i.e., phthalonitrile) and which exhibits lowered catalytic activity is brought into contact with hydrogen-containing gas at 200 to 500° C., and the rate of heating the catalytic hydrogenation catalyst is controlled to 40° C./min or less during the contact of the catalyst with hydrogen-containing gas, whereby the catalyst is regenerated, and the differential pressure of the catalyst layer is improved. The thus-regenerated catalyst is reused in hydrogenation of dicyanobenzene (see Patent Document 2).